Switched Ethernet technology and LAN switch

The development process of exchange technology

Ethernet switch, English for switch, also someone translates as switching, exchanger or switched hub. We first review the development of the local area network.

The combination of computer technology and communication technology has promoted the rapid development of computer local area network, from the advent of the Aloha in the late 60 to the 90-1000MBPS switched Ethernet, the 30-year period passed from simplex to duplex, from sharing to switching, from low speed to high speed, from simplicity to complexity, Leap from expensive to universal.

In the late 80, due to the rapid increase in traffic, prompting the development of technology, so that the performance of the local area network has become more and more high, the earliest 1MBPS rate has been widely replaced by today's 100base-t and 100cg-anylan, but, Traditional media access methods are limited to allow a large number of sites to share access to a public transport media, both CSMA/CD.

In the early 90, with the improvement of computer performance and the increase of traffic, the traditional LAN has been more and more exceeded its own load, the switching Ethernet technology came into being, which greatly improved the performance of LAN. Compared with the LAN topology of shared media based on bridge and router, the network switching function significantly increases the bandwidth. Switching technology to join, we can establish a geographically dispersed network, so that each port of the LAN switch can be parallel, secure and simultaneous transmission of information, and the LAN can be highly expanded.

From Network Bridge, multiport Network Bridge to switch

The development of local area network switching technology should be traced back to both ends of the network Bridge. A bridge is a storage and forwarding device for connecting to a similar LAN. Viewed from the structure of the Internet, the bridge is a DCE-level end-to-end connection; From the protocol level, the bridge is to store and forward the data frame in the logical link layer, which is similar to the function of the repeater in the first layer and the router in the third layer. The two-port Network bridge is almost simultaneous development with Ethernet.

Ethernet switching Technology (switch) is based on the Multiport Bridge and developed in the early 90, implementation of the OSI model of the next two protocols, and bridges are inextricably linked, and even by the industry known as "many connected bridge", so the current exchange technology is not a new standard, It's a new application of existing technology, an improved LAN bridge that offers more ports (4~88), better performance, stronger management capabilities, and cheaper prices than a traditional network bridge. Now some LAN switches also implement the OSI reference model of the third layer protocol, to achieve a simple routing function, the current very hot third-tier exchange refers to this. Ethernet switches are similar to telephone switches and provide additional bridging techniques, such as a pass-through (cut through), in addition to the storage and forwarding (store ANG ForWord) approach.

The working principle of switched Ethernet

The principle of an Ethernet switch is simple, it detects the source and destination Mac (media access layer) address of packets from the Ethernet port, then, compared with the dynamic lookup table in the system, if the Mac-level address of the packet is not in the lookup table, add the address to the lookup table and packages the data to the corresponding destination port.

Advantages of switched Ethernet Technology

Switched Ethernet does not need to change the network other hardware, including cable and user's network card, only needs to use the exchange switch to change the shared hub, saves the user network upgrades the expense.

It can transform between high speed and low speed network to realize the cooperation of different networks. At present, most switched Ethernet has 100MBPS ports, through the corresponding 100MBPS network card access to the server, the temporary solution to the bottleneck of 10MBPS, network LAN upgrade as the preferred solution.

It also provides multiple channels, more bandwidth than traditional shared hubs, traditional shared-10mbps/100mps Ethernet uses broadcast communication, can only communicate between a pair of users at a time, if collisions have to be retried, and switched Ethernet allows for transmission between different users, for example, A 16-port Ethernet switch allows 16 sites to communicate between 8 links.

In particular, the advantages of time response, so that the local area network switch favored. It provides bandwidth and high speeds over routers at a lower cost than routers, and switches have a tendency to replace routers unless there is a wide area network (WAN) requirement.

Straight-Through (cut Throuth), storage-Forwarding (Store-and-forward) comparison

The Ethernet network switch in direct mode can be understood as a line matrix telephone switch that is vertically and horizontally crossed between ports. When it detects a packet in the input port, it checks the packet's header, gets the destination address of the packet, launches the internal dynamic lookup table into the corresponding output port, connects the input and output intersection, and connects the packet to the corresponding port, realizes the Exchange function. Because there is no need for storage, delay (latency) is very small, the exchange is very fast, this is its advantage, its disadvantage is that because the contents of the packet is not saved by the Ethernet switch, it is not possible to check the transmission of packets are incorrect, can not provide error detection capabilities, because there is no cache, The input/output ports with different rates cannot be directly connected, and the exchange matrix becomes more and more complex when the port of the Ethernet switch is increased, which is difficult to achieve.

Storage and forwarding mode is the most widely used in the computer network field, it put the input port packets first stored, and then CRC check, after the error packet processing to remove the destination address of the packet, through the lookup table converted to output port packets sent. Because of this, storage and forwarding methods in the data processing time delay, this is its shortcomings, it can only access to the switch packet error detection, especially important is that it can support the different speed of the input and output ports between the conversion, to maintain high-speed port and Low-speed port cooperation between the work.

Second and third-tier exchanges and their competition with router schemes

The LAN switch is working on the second layer of OSI, can be understood as a multiport network bridge, so traditionally referred to as a second-tier exchange; At present, switching technology has extended to some functions of the third layer of OSI, which is called the third layer exchange, the third layer exchange can not spread the broadcast packet, directly using dynamically established MAC address to communicate , it seems to be able to read the third layer of information, such as IP address, ARP and so on, with multicast and virtual network based on IP, IPX and other protocol routing functions, this function of the smooth implementation of the special Integrated Circuit (ASIC) to join, the traditional software processing instructions to the ASIC chip embedded instructions, Thus, the forwarding and filtering of packets are accelerated, so that the linear Routing and service quality are guaranteed reliably at high speed. At present, if there is no need for wide area network, the expensive and limited bandwidth routers are not used in the construction project.